Blowback-type automatic and semi-automatic firearms have a common principle of operation which simply stated is this: A bolt reciprocates with respect to a barrel affixed to a body of the weapon to carry successive cartridges from a magazine into a rearward open breech of the barrel in position to be fired by a firing pin on the bolt. The explosive force of the fired cartridge propels the bolt rearwardly against the force of one or more compression springs. In a semi-automatic firing mode the bolt is caught by detent means in its rearward position and is moved forwardly by the spring for the next firing cycle only by operation of a trigger. In an automatic firing mode the bolt is propelled forwardly by the spring for repeated reciprocation and firing so long as the trigger is depressed.
Representative blowback-type automatic and semi-automatic firearms include the Beretta, the Uzi (see U.S. Pat. No. 4,335,643) and the Mendoza (see U.S. Pat. No. 3,906,833). Other blowback-type firearms include those shown in U.S. Pat. Nos. 4,019,423 and 2,437,548. In all of these prior art designs the bolt reciprocates back-and-forth in sliding engagement with a cylindrical interior surface of the gun body. It is generally the practice in these conventional designs to add the bolt, barrel and spring one-by-one to the gun assembly as all of the parts are put together, not necessarily in immediate sequence and not as a separate independent subassembly. Field assembly and disassembly is therefore relatively complicated. Foreign matter making its way to the slideable interface between the bolt and gun body can seriously impair the operation of the weapon, and cleaning is both necessarily frequent and painstaking.
The compression spring in most of the prior art blowback-type firearms is aligned axially rearwardly of the barrel and bolt and relies upon a cap at the end of the gun body to provide a spring abutment in opposition to the bolt. The weapon disclosed in U.S. Pat. No. 3,906,833 is an exception to this but all of the other prior art designs mentioned above include the rearward spring contained by the gun body. This appreciably lengthens the weapon and increases its weight.
It is a principal object of the present invention to provide a self-contained blowback-type firing unit, the barrel-spring-bolt subassembly of which is insertable as a discrete unit in and of itself in a gun body. While none of the aforementioned prior art designs teaches such a discrete firing unit subassembly it is to be noted that U.S. Pat. No. 4,327,626 discloses to some extent a combination of barrel-spring-bolt which is assembled together and then assembled within the remainder of the gun, though without carrying that concept to its highest advantage. That patent described a barrel having a rearward spring abutment and securing means for affixing the barrel to the gun body. A compression spring parallel to the barrel has a rearward end abutting the rearward spring abutment. Parallel to the spring and barrel is a reciprocable bolt having a forward spring abutment against which the forward end of the spring abuts and a firing pin base axially rearwardly of the barrel with apertures defined between the forward spring abutment and the base permitting entry and ejection of successive cartridges relative to the barrel breech. The bolt and barrel are in longitudinal slideable engagement.
However, while U.S. Pat. No. 4,327,626 teaches a spring between forward and rearward abutments on the barrel and bolt, it does not recognize the advantage of a self-contained discrete firing unit subassembly. This is clear from the fact that the prior art patent continues to employ the inner cylindrical surface of the gun body as a guide in slideable engagement with the bolt, indeed at a plurality of places, thereby leaving unsolved the problem of entry of dirt and consequent malfunction. In addition this prior art patent describes encircling the bolt in cylindrical and circumferentially complete sliding engagement around the barrel, thus making it highly vulnerable to jamming from differential thermal expansion as the hotter barrel swells within the encircling bolt. Further evidence that this prior art patent fails to recognize the potential of a discrete firing unit is that in addition to the spring operating between the bolt and barrel it teaches the use of a second spring in the conventional position rearwardly of the bolt abutted at its other end by a cap at the very end of the gun body with all the attendant disadvantages of added length and weight characteristic of other prior art blowback-type firearms.
A further disadvantage of the weapon described in U.S. Pat. No. 4,327,626, and all of the other prior art designs mentioned above, is that a draw-back element for manually cocking the bolt is exposed on the exterior of the gun body and can injure the operator as it reciprocates rapidly during automatic firing.
Yet another disadvantage of the prior art weapons with a rearward spring is that such a design shifts the center of gravity of the weapon rearwardly thus increasing the tendency of the barrel to buck upwardly in an uncontrolled fashion during recoil.
A further significant disadvantage in all of the prior art blowback-type automatic and semi-automatic firearms is their multiplicity of parts. Assembly and disassembly in the field is difficult and time-consuming and the likelihood of mechanical failure from entry of foreign matter or incorrect assembly is substantial.